WO2005064143A1

WO2005064143A1 - Method for real time determination of the mass of particles in a particle filter of a motor vehicle

Info

Publication number: WO2005064143A1
Application number: PCT/FR2004/050694
Authority: WO
Inventors: Shahin Hodjati; Christian Bert
Original assignee: Renault S.A.S.
Priority date: 2003-12-23
Filing date: 2004-12-15
Publication date: 2005-07-14
Also published as: JP2007515595A; JP4609815B2; FR2864146A1; EP1700021A1; US7319928B2; US20070150162A1; FR2864146B1

Abstract

The invention relates to a method for real-time determination of the mass of particles in a particle filter (3) fitted to the exhaust line (2) of an internal combustion engine (1). The following data - temperature T(t) of the exhaust gas at the filter input, oxygen [O2 (t)] and nitrogen oxide [NOx(t)] concentration of the exhaust gases entering the filter - is used to calculate the rate of combustion of the particles in the particle filter with the aid of kinetic laws of chemical reactions of particle combustion. Said rate, the rate emission of particles from the engine F(t) and the mass of particles in the filter mc(t-Δt) obtained during the cycle of operations prior to the moment t-Δt, is then used to calculate the mass of particles in the filter, mc(t): mc(t) = mc(t-Δt) + F(t) V(t)*Δt.

Description

The invention relates to a method for the real-time determination of the mass of particles present in a particle filter for the combustion engine of a motor vehicle. motor vehicle. The invention also relates to the use of this method in a management method for an engine, in particular engines operating in lean mixture. Indeed, the heterogeneity of the combustion processes in engines operating in a lean mixture has the effect of generating carbon particles which cannot be burned efficiently by the engine. This results in the appearance of black smoke at the exhaust; characteristics of this type of engine, in particular during starting phaseέ and during strong acceleration. Compliance with future legislative standards requires the implementation of deposition systems making it possible to completely eliminate particles as well as nitrogen oxides. Currently _" we have, at this. effect, of a semi-porous element forming a particle filter in the exhaust line, which allows the passage of the gauze x compounds while retaining the particulate compounds. In diesel engines, the fumes constitute the basic element of these particulate compounds. However, when the filter is deemed to be full, it is necessary to perform a purge in order to regenerate it. Thus, each particle retention phase must be followed by a regeneration phase during which the retained compounds are eliminated in non-polluting elements (carbon dioxide and water). A new phase of accumulation of particulate compounds can then begin. These particles are usually eliminated by combustion at a temperature of around 600 ^β C. However, the exhaust gases from these engines rarely reach such a temperature in normal operation: it is necessary to specifically increase the temperature during the regeneration. The means commonly used involve the creation of a gaseous environment heated to a temperature of about 600 ° C. This operation promotes self-ignition of the carbon particles retained in the filter. These are then consumed by releasing energy, which depending on conditions can be transmitted by weight to the particle bed in the filter, to the various components of the depollution system (particle filter, box and holding envelope, pipes, etc.), or else carried by the gas flow; from the engine. It is therefore important to know at all times the mass of particles contained in the filter, in particular after regeneration, so as to optimize the management of the progress of the regeneration phases and. to check the integrity of the filter. Indeed, the combustion of too large a quantity of particles can cause degradation or destruction of the filter due to the high exothermicity of this reaction. In general, the mass of particles present in the filter is estimated from the measurement of the pressure drop generated by the filter, as described for example in document PR-2 774 421. The mass; thus estimated, however, does not always have sufficient accuracy, so that the filter may be degraded. Document FR ~: 2,657,649 presents, for different operating conditions, different regeneration strategies and regeneration control. More precisely, this document proposes to use an estimator of mass of particles contained in the filter for setting in motion or stopping the different regeneration strategies used as a function of the speed and of the operating load of the engine.

The estimate of the mass of particles contained in the filter is determined using a difference between the mass of particles entering the filter from engine emissions and the mass of particles consumed by the combustion of particles in the filter. These masses are determined directly from maps as a function of the engine operating parameters, so that they also do not always have sufficient precision to avoid degradation of the filter. The invention aims to overcome these drawbacks by proposing a method for determining in real time the mass of particles present in a particle filter, which makes it possible to obtain an improvement in the precision of the calculation of the mass. The method according to the invention also has the advantage of requiring only one temperature sensor. inlet of the filter, which will therefore not be damaged in the event that the combustion of the particles is still too exothermic. To this end, the subject of the invention relates to a process for determining in real time the mass of particles present in a particle filter fitted to the exhaust line of an internal combustion engine, characterized in that the the following sequence of operations is repeated at determined time intervals: (i) the temperature T (t) of the exhaust gases at the inlet of the particle filter is measured at instant t using a sensor of temperature, (il) the operating parameters of the engine are measured at the instant t, by means of sensors, (iii) the instant at the time t, as a function of the operating parameters of the engine, is recorded on pre-established tables , the values of the following parameters: oxygen concentration [θ ₂ {£} j and nitrogen oxide concentration [NO _x {t}} of the exhaust gases entering the particle filter, the particle emission speed of the engine F (i) _} (iv) we calculate, using the kinetic laws chemical reactions of particle combustion, at time t, the rate of combustion V (t} of the inarticulate particles in the particle filter using the following parameters: temperature T (t), oxidant concentrations [θ ₂ { £}] i lNO _x {t)] _t and mass of particles present in the filter, m ₍ . (T-Δt), obtained during the previous operating cycle at time î-Δt, (v) we calculate , at. instant t, the mass of particles present on the filter, πicft), using the mass of particles πiçfi-Δt) obtained during the previous cycle of operations according to the following formula: fi) = m (t ~ Λt) + [F (t) ~ V (tj) * Δt _t o Δi is the time interval between the instants t-Δt and t, (vj) the value of the mass of particles m (t) present on the filter is recorded calculated at time t for use in the following sequence of operations at time t + t. In another embodiment, instead of reading one or more values of the parameters [ _a (i}) _^ [NO t)] _s F (t), we measure them _; by means of sensors. So, in case the three values are -measured by sensors, steps {"), {m) can be omitted. The invention also relates to the use of the method for determining in real time the mass of particles according to the invention, for; control and / or command a process for managing the regeneration of a motor vehicle particulate filter. The process according to ^; the invention making it possible to obtain a better evaluation of the mass of particles present in the filter at each instant, it is possible to prohibit the initiation of a regeneration if the quantity of particles detected risks endangering the integrity of the filter following an excessive rise in temperature at the time of combustion. In a variant, the determination method according to the invention is used when the temperature at the inlet of the filter is between approximately 250 ° C. and 500 ° C. Outside this temperature range, another method of mass determination can then be used, for example by using a pressure drop measurement in the â filter. particles. The invention also relates to the use of the method for determining in real time the mass of particles according to the invention, in a method for managing the regeneration of a particle filter of a motor vehicle, for determining a mass of threshold particles. for each operating point of a vehicle engine, below which the filter will tend to load with particles and beyond which the rate of combustion of particles in the filter will tend to increase. The invention is now described with reference to the accompanying non-limiting drawings, in which: -! Figure 1 is a schematic representation of an engine and its exhaust line equipped with a particle filter, -] Figure 2 is the plot of the mass of particles present in the filter calculated according to the method of invention ( _c ) and the mass of particles measured by weighing (trip) as a function of time. Referring to Figure 1, an engine 1 is connected to a gas exhaust line; 2 fitted with a particulate filter 3. Upstream of the filter 3, with respect to the direction of circulation of the exhaust gases, an oxidation catalyst 4 is installed on the exhaust line to oxidize the nitrogen monoxide of the exhaust gases to nitrogen oxides NO _* . I ^; A temperature sensor 5 is provided on the exhaust line, at the input of the particle filter 3. The engine speed sensors 6 and the engine load sensors 7 are provided at the engine level to measure the engine speed Ne ( number of revolutions per minute) and the engine load Q corresponding to depression of the accelerator pedal. Pressure sensors 8 and 9 are placed respectively at the inlet and at the outlet of the particle filter 3. The various sensors 5 to 9 are connected to a computer 10 in which: tables, or maps, characteristics of the engine are recorded. These tables are pre-established by preliminary measurements carried out for each engine. The method for determining the mass of rricft} particles present at instant î in the filter is now described. This process consists of. repeat at determined time intervals Δt the sequence of operations described below. (i) In a first operation, the temperature T (t) of the exhaust gases at the inlet of the particle filter is measured at instant t using the temperature sensor 5. The value obtained is recorded in the computer 10. fii) Substantially simultaneously, the operating parameters of the engine Ne and Q are measured at time t by means of the sensors 6 and 7. The measured values are also recorded in the computer 10. (iii) Then, the computer 10 uses pre-established tables which are functions of the values Ne and Q to read the values of the following parameters using as inputs the values Ne and Q measured at the instant t: oxygen concentration [θ ₂ (t)] and concentration nitrogen oxides; [NO _x . (T)] of the exhaust az entering the filter â. particles, and particle emission speed from engine F (î). These recorded values correspond to the values at time t and are recorded in the computer 10. 1! East. however, it is possible to replace this reading operation on tables with sensor measurements placed at the input of the filter to measure the concentrations of oxygen [θ ₃ (t) J and of nitrogen oxides [iYCλ, (t)] and by a measurement of a particle analyzer (also placed [at the inlet of the filter) to measure the particle emission speed of the engine F (t). Step (ϋ) can then be deleted. (iv) The computer 10 then proceeds to calculate the combustion speed V (t), at time t „of the particles in the particle filter.

As input data, the computer uses the parameters previously measured or recorded: temperature T {t), concentrations of nitrogen oxides μVO (t} J and oxygen [θ _a (£) j as well as the mass of particles present in the filter, πic (t-Δt), obtained during the cycle of operations preceding at time t-Δt For this purpose, the computer uses the kinetic laws of the chemical reactions of particle combustion, the formulas of which are These laws will be detailed later. (v) In the following operation, the calculator calculates the mass of particles present on the filter at time t, rricft), using the mass of particles obtained during the cycle of operations preceding at time i- Δi, mç (t-Δt) _t according to the following formula: rhcft} ≈ nic (i-Δt} + \ F (t} ~ V (t)} * Δt _s (E ) where Δt is the time interval between the instants t-Δt and t (vi) The value of ia mass of particles rrt fi) present on the filter calculated at l 'instant t is then saved to be used as a value ^; entry into the following sequence of operations at time t + Δt, in particular in operations fiv) and (v). The sequence of operations described above is then executed again at time t + _ t At the initial time tt, no mass πic (i-Δt) is available, the computer then uses a mass of particles present on the filter m _pr χ _> {ti) estimated using the pressure drop or pressure difference ΔP at the time ti between the inlet and the outlet of the filter 3 in a conventional manner. This pressure difference is for example calculated using as input values the measurements of the pressure sensors 8 and 9. i it is also possible to have recourse to this estimated mass of particles m _P r sswn at later times i of operation of the engine, for example for the purpose of checking the calculated mass m _c (t) according to the method of the invention. ^! The mass of particles present on the filter is thus corrected in real time as a function of the operating point of the engine, which makes it possible to achieve a precision much higher than the known methods of determining the mass. We will now decipher the kinetic laws used by the third computer according to the invention. The combustion reaction of the particles (soot) in a catalyzed particle filter (active phase of the filter comprising a catalyst), is initiated according to three different and complementary processes: (1) The first process corresponds to the combustion of the particles by oxidation by the nitrogen oxides NO _X contained in the exhaust gases or formed by the reaction of nitrogen monoxide on platinum sites present in the active phase deposited by the filter. This

<reaction takes place in the range of 250 to about 50 ° C, (2) The second process corresponds to the action of the phase catalyst; filter active. The catalyst has an oxygen donor character and provides oxygen for the oxidation of the particles. This process begins around 350 ° C. (3) The third process corresponds to the combustion of the particles by the oxygen present in the exhaust gases, initiated around 450 ~ 5G0 ° C, this process intensifies with the temperature and is responsible in particular for the active regeneration of the filter around 600 ° C. The reaction rates of these different processes can be put into kinetic equations in the following form (the rates are expressed in g / s):

Process (1): VAO. ≈ rA ^{£ Q! / Rr!} "x" - Δt) f ^l - [NO _x {t) f

Process (2): Y _o ^^ ≈ Kie - *** ™ [ _e (t - Δt) x [θ _2œ ^ _seîJr (t) Process (3): 1A = K ^ ** x [m _e (t - At) f ² * [θ ₂ (t) f •In which :

^' i- T (t) represents the. temperature measured at the input of the filter, τrto {t-Δt) represents the mass of particles (in grams) present on the filter at time t-Δt and calculated during the sequence of operations previously executed,

- {NOxft}} represents the concentration of nitrogen oxides (in pprn) in the exhaust gases entering the filter at time t,

¹ lθ ct iys ur (t)} represents the. oxygen concentration (in percentage) available in the active phase f'wash coat ") at time t,

- [OzftJl represents the oxygen concentration (in percentage) in the exhaust gases entering the filter at time t,

- JO, Kz, K3 are the pre-exponential factors of the combustion reactions of the processes (1), (2), (3) respectively, - Eal. Ea2, Ea3 are the activation energies of the combustion reactions of the processes (1), (2), (3) respectively,

- al, a2, a3 _> £>, c, d are the partial orders of the reactions with respect to the mass of soot and the oxidant (NO _x or Os),

- ï? is the constant of ideal gases. The kinetic parameters Kι _f K2 _S K3, Eal, Ea2, Ea3, al _f α2 a3, hc, d, are determined experimentally in a conventional manner. In the case of the first speed equation: V _NOi = ^j r _lβ ^ ™ x [m _c (i - άtjf ¹ {NO _x (t} f _f . The following values can be used (for x ≈ 2): 1 -5000 <Eal / R <-20O0! Θ, 2 <al <ï: O, 2 <b <2 The pre-expon ial factor Ki varies according to the nitrogen oxide concentration: 'Si [NOs (t)} > 90 pprn: K, = | NO _a {t} fxm) - VO _a (t) ^χ n]) + p; θû: 10-s <m <10-6 10-6 ^. < _n <10- "10 ^ <p <0-2, If [NOsftfi <90 pprn: K _} " q where 1O ^& <q <10 ~ ³ . In the case of the second speed equation:

≈ _Λ e- * ^{> v} * ™ x [m _c {t - At) f ² x

the following values can be used: ~ 250Q <Eα2 / .R <~ lO0Q 1 <a2 <2,5: O <c <1,5: The pre-exponential factor K2 varies according to the input temperature in the filter or the amount of oxygen:; If Tft)> 260 ° C; K ≈ τ {î} fxj) ~ (| r (f} χ fcj + 1; WHERE: 10-9 <j < ₁₀ -7 10- ⁶ <Je <10- ^{4 "} 10- ³ <ι <1.0- ² , ; If rt <260 ^β C or

<4.6%: K ₃ ~ i where O <i <0.2.

In the case of the third speed equation: V _0χ - K ^ - * "*** ™ x [rn _c (t - Δîf ³ x [θ ₂ (t) the following values can be ^used:; -25000 <Ea3 / R <- I 0000: 0.5 <α3 <2 0 <d <1.5 i if (O2) <4.6% tf, ≈ e * where 15 <gf <30. otherwise K ₃ -n where 0 <n <0.2 These parameters, as well as the formulas for the kinetic velocities, are recorded in the computer 10 and used to calculate the combustion speed V {t) of the particles in the filter. This speed V {i) is the "form of the speeds of the three processes:: V {t)" ^ Λ'O, ⁺ ^ O- ⁺ ^ atalseu _ It will be understood, that in this case, only the concentrations f Ox ^ j jet fOs ^(t) ] can possibly be measured by sensors,

Step (ii) of measuring the engine operating parameters (Ne, Q) cannot then be deleted. ! When the filter 3 does not include a catalyst, then the combustion reaction according to process (2) does not occur. Speed; combustion temperature is then: ^{A (} AA ^ The value of the combustion speed thus calculated can be used for the calculation of the mass of particles present in the filter τn, - (t), eh using equation (E). ^'Figure 2 shows. good adequacy between the mass of particles calculated according to the method of the invention (mΛ and the mass of particles actually present in the filter and determined by weighing {m _P ). ^• : The sequence of operations used to calculate the mass of particles according to the invention is preferably executed at time intervals ai of the order of one second. Of course, other values can be used.

Claims

; CLAIMS it. Method for determining in real time the mass of particles present in a particle filter (3) fitted to the exhaust line (2) of an internal combustion engine (1), characterized in that repetitions are made time intervals Δt determined the following sequence of operations: (i) the temperature T (î) of the exhaust gases at the inlet of the particulate filter (3) is measured at instant r using a temperature sensor (5), (ϋ) the operating parameters of the engine (Ne, Q) are measured at the instant t by means of sensors (6, 7), (iii) the measurement is made at the instant t, as a function of the parameters of engine operation (Ne, Q), on pre-stage tables, the values of the following parameters: oxygen concentration jp ₂ (r) j and nitrogen oxide concentration O _x (t) j of the exhaust gases entering the particle filter, the particle emission speed of the engine F (t),. (iv) using the kinetic laws of the chemical reactions of combustion of the particles, the combustion speed V (t) of the particles in the particle filter is calculated using the following parameters: temperature T (t), oxidant concentrations

₁ ^ ₂ ^)] ^: l ^ _v W], and mass of particles present in the filter ,. mc (t ~ Δt), obtained during the cycle of operations preceding at time t-Δt, () we calculate, at time t, the mass of particles present on the filter, r cft), using the mass of particles πic (t-Δt) obtained during the previous cycle of operations according to the following formula: (t) ≈ m _c (t ~ Δt) + [F (t) - V (t)) * Δt, where Δt is the time interval between the instants t-Δt and t, (γi) -we record the value of the mass of particles mc (t) present on the filter calculated at time t for use in the sequence d 'following operations at time t + Δt. 2. Method according to claim 1, characterized in that, instead of reading one or more values of the parameters [Os (^) J _ι [^ O _x (f}] _t F (t} _t on pre-established tables , or they are measured by means of sensors. 3v Method according to claim 1 or 2, characterized in that, for the calculation of the combustion rate V (t), the combustion reactions of the particles by the oxides d NOx nitrogen and by oxygen Oa, the rate of combustion being the sum of the rates of reactions of combustion of particles by nitrogen oxides V, _Vo - and pa oxygen ^ _0j • pu; V _{NO ^ ≈ ιe} - * ". '≈r (., _Χ [ _m . _{T „ _Δt) j ^. Ι _χ [ _/ vo _^ ^ f

: _0Ï = if ₃ - ^{£ oa} ' ^îfîriî! x [m _c (t - Δî)] " ³ x [θ _? (t)] ^d where Tïλ

[ΛO _A. (T ^; ) | are determined during the previous operation (iii), ai, a3, b and d are the partial orders of the combustion reactions, and Eal and Ea3 are the activating energies. combustion reactions with nitrogen oxides and oxygen respectively. 4. Method according to claim 3, in which the particle filter comprises an active phase for catalyzing the combustion of the particles, characterized in that, when calculating the combustion rate, the combustion reaction of the particles is also considered by the oxygen present in the active phase of the particulate filter, la. combustion rate being the sum of the rates of combustion reactions of the particles by the nitrogen oxides v _m , by the oxygen V _{0 ^} and by the oxygen in the active phase V ^^, _^ . . V {t) ≈ V _M , + v ^ + v _c ^ _{a (a! SιW} OÙ * < _3j c "aβ _f t * $ e" r ≈ K ₂ ^{β '} X [m _c (t ~ At}} X i zca _t a _l yseur Wj o lθ _2œtα j _ysβur (t) J is the oxygen concentrat in the active phase of the filter measured on a pre-established table during a previous operation depending on the engine operating parameters

(Ne, Q at time t, a2 and c are the partial orders and Ea.2 the energy of activation of the combustion reaction by oxygen of the active phase.: 5. Method according to one of Claims 1 to 4, characterized in that, at the initial instant tt, the mass of particles present in the filter mc (î-Δt) used in operations (iv) and. (v) is replaced by a mass of particles present in the filter {m _pr ession (t estimated from a measurement, at time & -, of the pressure drop between the inlet and the outlet of the filter.

.6. Method according to. claim 5, characterized in that the mass of particles present in the print filter) estimated from a measurement of the pressure drop between the inlet and. the filter output is used in operations (iv) and (v) at a time t different from the initial time 7. Method according to one of claims 1 to 6, characterized in that ia _: measurement of the operating parameters of the engine comprises the steps consisting in: _t sensing the speed of rotation of the engine, Ne, using a speed shooting sensor (6), - sensing the. engine load, Q, using a load sensor (7). ; S. Use of the determination method according to one of the preceding claims, for controlling and / or controlling a method for managing the regeneration of a particulate filter of a motor vehicle. 9. Use according to claim 8, in which the determination method is used when the temperature at the inlet of the filter is between approximately 250 ° C and 500 ° C. 10. Use of. determination method according to one of claims 1 to. 7, in a method for managing the regeneration of a motor vehicle particle filter, to determine a m se! of threshold particles for each operating point of the engine of a vehicle, below which the filter will tend to load into particles and beyond which the rate of combustion of the particles in the filter will tend to increase.